LINQ元素操作符

除了DefaultIfEmpty，其余八种标准查询元素运算符从集合返回单个元素。

查看示例

ElementAt示例- Enumerable.ElementAt方法

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Operators
{
  class Program
  {
     static void Main(string[] args)
     {
        string[] names =
              { "Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow", 
                "Hedlund, Magnus", "Ito, Shu" };
        Random random = new Random(DateTime.Now.Millisecond);

        string name = names.ElementAt(random.Next(0, names.Length));

        Console.WriteLine("The name chosen at random is '{0}'.", name);
        Console.ReadLine();
     }
  }
}

VB

Module Module1
  Sub Main()
     Dim names() As String = _
           {"Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow", "Hedlund, Magnus", "Ito, Shu"}

     Dim random As Random = New Random(DateTime.Now.Millisecond)

     Dim name As String = names.ElementAt(random.Next(0, names.Length))

     MsgBox("The name chosen at random is " & name)
  End Sub
End Module

当C＃或VB的上述代码被编译和执行时，它产生了以下结果：

The name chosen at random is Ito, Shu

注： - 在这里，上面的输出会动态变化和名称会被随机选择。

First示例- Enumerable.First方法

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Operators
{
  class Program
  {
     static void Main(string[] args)
     {
        int[] numbers = { 9, 34, 65, 92, 87, 435, 3, 54, 
                          83, 23, 87, 435, 67, 12, 19 };

        int first = numbers.First();

        Console.WriteLine(first);
        Console.ReadLine();
     }
  }
}

VB

Module Module1
  Sub Main()
     Dim numbers() As Integer = _
              {9, 34, 65, 92, 87, 435, 3, 54, 83, 23, 87, 435, 67, 12, 19}
      
     Dim first As Integer = numbers.First()

     MsgBox(first)
  End Sub
End Module

当C＃或VB的上述代码被编译和执行时，它产生了以下结果：

9

Last例子- Enumerable.Last方法

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Operators
{
  class Program
  {
     static void Main(string[] args)
     {
        int[] numbers = { 9, 34, 65, 92, 87, 435, 3, 54, 
                          83, 23, 87, 435, 67, 12, 19 };

        int last = numbers.Last();

        Console.WriteLine(last);
        Console.ReadLine();
     }
  }
}

VB

Module Module1
  Sub Main()
     Dim numbers() As Integer = _
              {9, 34, 65, 92, 87, 435, 3, 54, 83, 23, 87, 435, 67, 12, 19}
      
     Dim last As Integer = numbers.Last()

     MsgBox(last)
  End Sub
End Module

当C＃或VB的上述代码被编译和执行时，它产生了以下结果：

19

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